Condensed Consolidated Statement of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Common shares	Treasury shares	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)			(11,000,000.0)
Common shares, issued (in shares)		65,200,000
Total shareholders' equity at Sep. 30, 2019	$ 1,303.5	$ 0.7	$ (803.8)	$ 1,627.7	$ 714.8	$ (235.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	46.6				46.6
Foreign currency translation adjustments	8.1					8.1
Pension and postretirement activity, net of tax	(1.8)					1.8
Deferred gain (loss) on hedging activity, net of tax	(1.5)					(1.5)
Activity under share plans (in shares)			100,000
Activity under share plans (in usd)	13.3		$ 11.7	1.6	0.0
Total shareholders' equity at Jun. 30, 2020	1,368.2	$ 0.7	$ (792.1)	1,629.3	761.4	(231.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)			(10,900,000)
Common shares, issued (in shares)		65,200,000
Total shareholders' equity at Mar. 31, 2020	1,347.3	$ 0.7	$ (793.5)	1,626.1	756.7	(242.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	4.7				4.7
Foreign currency translation adjustments	14.5					14.5
Pension and postretirement activity, net of tax	(1.1)					1.1
Deferred gain (loss) on hedging activity, net of tax	(1.8)					(1.8)
Activity under share plans (in shares)			0
Activity under share plans (in usd)	4.6		$ 1.4	3.2	0.0
Total shareholders' equity at Jun. 30, 2020	$ 1,368.2	$ 0.7	$ (792.1)	1,629.3	761.4	(231.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)			(10,900,000)
Common shares, issued (in shares)		65,200,000
Treasury shares (in shares)	10,896,806		(10,900,000)
Common shares, issued (in shares)	65,251,989	65,200,000
Total shareholders' equity at Sep. 30, 2020	$ 1,432.9	$ 0.7	$ (790.4)	1,631.8	782.4	(191.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	72.9				72.9
Foreign currency translation adjustments	23.0					23.0
Pension and postretirement activity, net of tax	(1.3)					(1.3)
Deferred gain (loss) on hedging activity, net of tax	3.5					3.5
Dividends declared to common shareholders	(25.4)				(25.4)
Treasury shares repurchased (in usd)	$ (9.2)		$ (9.2)
Treasury shares repurchased (in shares)	(300,000)		(300,000)
Activity under share plans (in shares)			300,000
Activity under share plans (in usd)	$ 15.2		$ 22.3	(7.1)	0.0
Total shareholders' equity at Jun. 30, 2021	1,511.6	$ 0.7	$ (777.3)	1,624.7	829.9	(166.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)			(10,900,000)
Common shares, issued (in shares)		65,200,000
Total shareholders' equity at Mar. 31, 2021	1,464.1	$ 0.7	$ (781.3)	1,622.0	797.7	(175.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	40.8				40.8
Foreign currency translation adjustments	9.1					9.1
Pension and postretirement activity, net of tax	(0.7)					(0.7)
Deferred gain (loss) on hedging activity, net of tax	0.2					0.2
Dividends declared to common shareholders	(8.6)				(8.6)
Activity under share plans (in shares)			0
Activity under share plans (in usd)	6.7		$ 4.0	2.7	0.0
Total shareholders' equity at Jun. 30, 2021	$ 1,511.6	$ 0.7	$ (777.3)	$ 1,624.7	$ 829.9	$ (166.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)	10,893,360		(10,900,000)
Common shares, issued (in shares)	65,251,989	65,200,000